1. Field of the Invention
The present invention relates to an automatic tool changer for automatically changing a tool in a machine tool.
2. Description of Related Art
As a device for automatically changing a tool to be fixed to the spindle of a machine tool, an automatic changer, in which an impact generated during tool change is lessened, and the moving amount of a spindle head during tool change is reduced, was already developed by the applicant and has been well known (see JP6-739A).
FIG. 1 is a schematic view of this automatic tool changer. The automatic tool changer has a vertically movable arm member 4, a turret 13 having a plurality of tool grippers 12 and holding tool holders 11 (tools). The turret 13 is provided with a speed reducer 5 for selecting a desired tool through the allocating operation, and the tool grippers 12 are so constructed as to rotate to be maintained in a tool change position due to the output of the speed reducer 5. A spindle 2 to which the tool holders (tools) 11 are fixed is rotatably supported by a spindle head 1.
The spindle head 1 has swing cams Csa and Csb for swinging the turret 13 in order to move each of the tool holders 11 held by the corresponding tool gripper 12 to a position where it is fixed to the spindle 2, and a lift cam CL for mounting and detaching the tool holder 11 with respect to the spindle 2 by moving the turret 13 up and down to move the corresponding tool gripper 12 in the vertical direction. The tool grippers 12 are fastened to a flange of a driven plate of the speed reducer disposed in the turret 13. Biasing means 18 is fixed in the middle portion of a turret base 13a with a fixing pin. One end of the turret base 13a is fixed to a turret slider 16 through a rotary shaft 20, and a swing roller 17 that cooperates with the swing cams Csa and Csb is rotatably fitted in the end portion on the opposite side of the rotary shaft 20. The biasing means 18 is fixed in the middle portion of the turret base 13a with the fixing pin, and the turret base 13a is biased anticlockwise around the rotary shaft 20. The swing roller 17 is so constructed as to be biased against cam faces of the swing cams Cs by the biasing means 18. With this structure, the swing roller 17 is supported by the swing cams Csa and Csb to be moved relatively on the swing cams Csa and Csb, to thereby swing the turret 13 according to the shapes of the swing cams Csa and. Csb.
The rotary shaft 20 is coupled to the turret slider 16. The turret slider 16 is constructed vertically movable along a linear guide, not shown, which is fixed to the arm member 4. A lift-adjusting member 15 is fixed to the other end of the turret slider 16 with a ball joint 10, and a lift lever 14 is fixed to the other end of the lift-adjusting member 15. The lift lever 14 is bent at an angle of about 90 degrees and is rotatably fitted to the arm member 4 at its bending point. A lift roller 9 engaged with the lift cam CL is rotatably fitted to the other end of the lift lever 14. In FIG. 1, reference numeral 3 represents a spindle motor for driving the spindle.
With the above-described structure, once a tool change command is given, the orientation of the spindle is carried out. At the same time, the spindle head 1 moves upward at fast speed, and the swing roller 17 moves on a flat supporting surface of the swing cam Csa (FIG. 1 shows a position where the spindle head 1 is raised. Before tool change operation is started, the spindle head 1 is in a descended position, whereas the turret 13 is positioned in an upper position in relation to the spindle head 1, and the swing roller 17 is positioned in an upper end portion of the swing cam Csa). The lift roller 9 moves in a straight-line portion of the lift cam CL, and the lift operation is not performed. Subsequently, due to the upward motion of the spindle head 1, the swing roller 17 moves in a curved portion of the swing cam Csa, thereby turning the turret base 13a anticlockwise around the rotary shaft 20 and beginning the swing motion of the turret 13. The tip end of the tool gripper 12 approaches a V-groove of the tool holder 11. After a roller provided to the tip end portion of the tool gripper 12 is engaged with the V-groove, the roller accurately moves on the V-groove.
Furthermore, due to the upward motion of the spindle head 1, the swing roller 17 moves to a flexion of the swing cam Csa and the swing cam Csb. Immediately before the swing motion therebetween is finished, the lift roller 9 is engaged with a flexion of the lift cam CL, thereby turning the lift lever 14 anticlockwise around the rotary shaft, moving the lift-adjusting member 15 and the turret slider 16 in the upward direction, and accelerating the turret base 13a, namely the turret 13, in the same direction with respect to the upward motion of the spindle head 1. As a result, when the swing motion is finished, due to the upward motion of the spindle head 1 and the lift operation of the turret 13, the relative speed becomes virtually zero, so that the impact is drastically reduced.
After the swing motion is finished, the spindle head 1 moves upward at fast speed, and simultaneously the turret 13 begins the lift operation for pulling out the tool holder 11 from the spindle. In other words, the swing roller 17 moves on the swing cam Csb, and the lift roller 9 moves from the top of the flexion of the lift cam CL in a descending direction. This makes the swing motion slight. Additionally, since the lift roller 9 moves in the opposite direction to the direction of moving to the top of the lift cam CL, the lift acceleration acts in the opposite direction, which slows down the upward lift operation. The downward lift operation is started. Due to the relative downward lift operation with respect to the spindle head 1, the tool holder 11 is pulled out from the spindle 2.
After the upward motion of the spindle head 1 is finished, a spindle gear 19 of the spindle 2 and a turret gear 5c of the speed reducer 5 are engaged with each other. The spindle 2 rotates to rotate the turret 13 through the speed reducer 5, to thereby carry out the allocation of the desired tool. After the turret-allocating operation is finished, the spindle head 1 descends in the inverse order to the above-mentioned order, and the tool change operation is completed.
FIG. 5 are explanatory views of the speed reducer used in the above-described conventional automatic tool changer. The speed reducer is formed of a holder 51, a driving plate 52, and a driven plate 53. As shown in FIG. 5c, the driving plate 52 is provided with cogs in its circumferential surface to serve as a turret gear 5e. In the end face of the driving plate 52, a circular cam groove 52a with radius r is formed to be eccentric from the rotational center of the turret gear 5e by an eccentricity amount Q. In the holder 51, as shown in FIG. 5b, n+1 oval groove portions 51a extending longitudinally along the radial direction are arranged at regular angle intervals on the condition that the speed reduction ratio is n (n=2, 3, 4 . . . ). The examples illustrated in FIG. 5 show the case where the speed reduction ratio n equals 6. The longitudinal length of each of the oval groove portions 51a along an axis is twice or more as great as the eccentricity amount Q in the eccentric circular cam groove 52a of the driving plate 52. Balls 54 are held in the respective groove portions 51a. On the surface of the driven plate 53, as shown in FIG. 5a, there is provided a virtually circular member having a cam groove 53a in the shape of petals or a starfish including as many concaves and convexes as the speed reduction ratio n in the radial direction, engaging with the balls 54. The examples of FIG. 5 show the case where the speed reduction ratio is 6.
The driving plate 52 is rotatably fitted to the turret base 13a, and the holder 51 is fixed to the turret base 13a in a state superposed upon the driving plate 52. The oval groove portions 51a of the holder 51 are made to hold the respective balls 54, and the balls 54 and the cam groove 52a of the driving plate 52 are engaged with each other. Moreover, the driven plate 53 is fitted to the holder 51 to be rotatable and superposed thereupon. The cam groove 53a of the driven plate 53 and the balls 54 held by the holder 51 are engaged with each other. The tool grippers 12 are fixed to the driven plate 53.
While the driving plate 52 makes one rotation, the balls 54 make one reciprocating motion in the radial direction within the respective groove portions 51a of the holder 51 in the state engaged with the cam groove 53a of the driven plate. As to the motion of the balls 54 within the groove portions 51a, in the cam groove 53a of the driven plate 53, the balls 54 for example move from the top to the top and press the side faces of the cam groove 53a between the tops, to thereby move the driven plate 53 for one cycle of the cam groove 53a. In other words, since the number of concaves and convexes of the cam groove 53a is n, the driven plate 53 moves only by 2π/n with respect to a center angle φ. Therefore, if the speed reduction ratio is 6, the driven plate 53 makes ⅙ rotation while the driving plate 52 makes one rotation, making it possible to obtain ⅙ speed reduction.
In the above-described conventional automatic tool changer, when the turret 13 is rotation-driven, the load is great, so that it is necessary to moderate the acceleration/deceleration. Furthermore, abrasion of the balls 54 of the speed reducer and a pressing force of the balls 54 are unevenly generated. As a result, there arises the problem that undulation occurs in the rotation of the turret.
As described, with the speed reducer used in the conventional automatic tool changer, the cam groove 52a formed in the driving plate 52 has the circular shape as shown in FIG. 5, so that the degree of freedom in design is small, and it is impossible to set a sufficiently small pressure angle. In order to decrease the pressure angle, the eccentricity amount Q of the cam groove 52a of the driving plate 52 is made large to increase the motion amount of the balls 54. By so doing, however, there generates an undercut in the cam groove 53a of the driven plate 53, or a curvature radius of the cam groove 53a of the driven plate 53 becomes extremely small. Therefore, the pressure angle should not be reduced. Due to the great pressure angle, the load created when the turret is rotation-driven is great, so that it is necessary to moderate acceleration/deceleration in order to smooth the turret rotation. Therefore, the tool change takes time.
Furthermore, because of the eccentricity of the cam groove 52a of the driving plate 52, the axial pressing force borne by each of the balls 54 becomes eccentric and uneven, so that the surface pressure borne by each of the balls is locally increased. As a result, the cam grooves 52a and 53a or balls abrade away, and occasionally do not last for a full duration of life. Moreover, since the balls 54 are unevenly distributed with respect to the surfaces of the driving plate 52 and the driven plate 53, due to deviation in the axial pressing force borne by each of the balls 54, there generates undulation during the rotation of the driving plate 52 due to the eccentricity of the axial pressing force borne by each of the balls 54. Consequently, when the spindle-side gear 19 and the turret gear 5e rotate in the state engaged with each other, a backlash in cog surfaces of the gears fluctuates, so that the backlash cannot be properly regulated. As a consequence, there is the problem of loud noises.